Genetic linkage studies in early onset-familial Alzheimer's disease (AD) families have determined that mutations in at least three loci will cause the disease: the amyloid beta-protein precursor gene, the presenilin-1 gene (PS-1), and the presenilin-2 gene (PS-2). While it has been reported that beta-amyloid production is abnormal in fibroblasts from families carrying PS-1 and PS-2 mutations, and a homologues protein in C. elegans affects Notch signaling, the function of the presenilin gene is presently unknown. Therefore, the long-term objective of this application is to determine the function of the presenilin protein and other presenilin- interacting proteins. Drosophila melanogaster is an ideal model organism for determining the function of uncharacterized genes, which in this case is made even more ideal as most studies of Notch signaling have been carried out in Drosophila. Using the high conservation among conservation among presenilin genes, our lab has successfully coned the gene in Drosophila. The first specific aim of this project will be to characterize this gene in Drosophila, studying its gene structure, its developmental transcription pattern, and its localization in embryos, larvae, pupae, and adult flies, DNA sequencing. Southern and Northern blotting techniques, and light microscopy will be used to carry out this part of the project. The second specific aim will be to produce null mutations of this gene and study their effects in Drosophila. P-element insertion mutagenesis will be used to produce the mutant flies, and the flies will be characterized genetically. The third specific aim will be to determine which genes interact with the presenilin gene. Fly genetics and yeast two-hybrid approaches will be used to find these presinilin- interacting genes. This project will lead to a greater understanding about the biology and function of the presenilin genes, the major cause of early- onset familial Alzheimer's disease. By determining the functions of the presenilins, and their interactions with other genes, a greater understanding of the pathogenesis of AD will be gained, which may lead eventually to improved treatment of the disease. Additionally, a long- term study of these presenilin-interacting proteins will help us to identify other human loci which may cause or influence AD in both early-onset and late-onset cases.